1. Field of the Invention
The present invention relates to a resist removing method and a resist removing apparatus for removing an unnecessary resist from a surface of any of various substrates such as semiconductor wafers.
2. Description of the Related Art
Semiconductor device production processes generally include the steps of selectively etching an oxide film and the like formed in a surface of a semiconductor wafer (hereinafter referred to simply as “wafer”), and locally implanting an impurity (ions) such as phosphorus, arsenic or boron into the surface of the wafer. In these steps, a resist pattern of an organic compound such as a photosensitive resin is formed on an outermost surface of the wafer for prevention of the etching or the ion implantation to an undesired portion of the wafer, whereby the portion undesired to be subjected to the etching or the ion implantation is masked. After the etching or the ion implantation, the resist present on the wafer becomes unnecessary. Therefore, a resist removing treatment is performed for removing the unnecessary resist from the wafer after the etching or the ion implantation.
Exemplary methods for the resist removing treatment include a batch treatment method in which a plurality of substrates are treated in a batch, and a single substrate treatment method in which substrates are treated one by one. Conventionally, the batch treatment method has been predominant. However, the batch treatment method requires a treatment bath having a volume sufficiently great to accommodate the plurality of substrates. Further, the substrates to be treated tend to have an increased size. Therefore, the single substrate treatment method is attractive without the need for the greater-volume treatment bath.
In the resist removing treatment by the single substrate treatment method, an SPM (sulfuric acid/hydrogen peroxide mixture) which is a mixture of sulfuric acid and hydrogen peroxide water is supplied to a center portion of the surface of the wafer, while the wafer is rotated at a predetermined rotation speed about a rotation axis extending through the center of the wafer. The SPM supplied to the wafer surface flows from the center portion to a peripheral edge of the wafer on the wafer surface to quickly spread over the entire wafer surface by a centrifugal force generated by the rotation of the wafer. The resist present on the wafer surface is lifted and removed from the wafer surface by a strong oxidation power of Caro's acid (peroxosulfuric acid) contained in the SPM. After the removal of the resist from the wafer surface, pure water is supplied to the wafer surface to rinse away the SPM adhering to the wafer. Thereafter, the wafer is rotated at a higher speed for drying. Thus, the resist removing treatment sequence is completed.
The inventor of the present invention conducted a study in which the number of particles adhering to the wafer surface was determined by means of a particle counter immediately after the resist removing treatment, and found that virtually no particle was detected immediately after the treatment but, after a lapse of several hours from the completion of the treatment, several tens of thousands particles were detected.